Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.45	3.467%	$57.3725	$57.37	$57.35	$57.40
Purchase #2	$50.79	13.126%	$57.4567	$57.46	$57.45	$57.50
Purchase #3	$87.57	6.376%	$93.1535	$93.15	$93.15	$93.20
Purchase #4	$231.92	13.509%	$263.2501	$263.25	$263.25	$263.30
Purchase #5	$90.60	4.448%	$94.6299	$94.63	$94.65	$94.60
Purchase #6	$205.50	12.583%	$231.3581	$231.36	$231.35	$231.40
Purchase #7	$69.28	13.142%	$78.3848	$78.38	$78.40	$78.40
7 purchase totals =	$791.11		$875.6056	$875.60	$875.60	$875.80